LESSON 6.] RUNNERS, TENDRILS, SPINES. 39 



Squash tribe are familiar illustrations. The tendril commonly grows 

 straight and outstretched until it reaches some neighboring support, 

 such as a stem, when its apex hooks around it to secure a hold ; 

 then the whole tendril shortens itself by coiling up spirally, and so 

 draws the shoot of the growing plant nearer to the supporting object. 

 When the Virginia Creeper climbs the side of a building or the 

 smooth bark of a tree, which the tendrils cannot lay hold of in the 

 usual way, their tips expand into a flat disk or sucker (Fig. 62, G3), 

 which adheres very firmly to the wall or bark, enabling the plant to 

 climb over and cover such a surface, as readily as the Ivy does by 

 means of its sucker-like little rootlets. The same result is effected 

 by different organs, in the one case by branches in the form of ten- 

 drils ; in the other, by roots. 



93. Tendrils, however, are not always branches ; some are leaves, 

 or parts of leaves, as those of the Pea (Fig. 20). Their nature in 

 each case is to be learned from their position, whether it be that of 

 a leaf or of a branch. In the same way 



94. Spines or Thorns sometimes represent leaves, as in the Bar- 

 berry, where their nature is shown by their situation outside of an 

 axillary bud or branch. In other words, here they have a bud in 

 their axil, and are therefore leaves ; so we shall have to mention 

 them in another place. Most commonly spines are stunted and 

 hardened branches, arising from the axils of leaves, as in the Haw- 

 thorn and Pear. A neglected Pear-tree or Plum-tree shows every 

 gradation between ordinary branches and thorns. Thorns sometimes 

 branch, their branches partaking of the same spiny character : in 

 this way those on the trunks of Honey-Locust trees (produced from 

 adventitious buds, 58) become exceedingly complicated and horrid. 

 The thorns on young shoots of the Honey-Locust may appear some- 

 what puzzling at first view; for they are situated some distance 

 above the axil of the leaf. Here the thorn comes from the upper- 

 most of several supernumerary buds (59). Prickles, such as those 

 of the Rose and Blackberry, must not be confounded with thorns : 

 these have not the nature of branches, and have no connection with 

 the wood ; but are only growths of the bark. When we strip off 

 the bark, the prickles go with it. 



95. Still stranger forms of stems and branches than any of these 

 are met with in some tribes of plants, such as Cactuses (Fig. 7G). 

 These will be more readily understood after we have considered 

 some of the commoner forms of 



